This invention relates to seam adjusters and, in particular, it relates to adjusters for seamers to ensure that a tight seam is formed between a can end and a can body and that seam tightness is reproducible over long manufacturing runs.
Seaming technology is well established for forming typically a double seam in which a top or base can end component is rolled onto the can body flange in two operations. The can end has a seaming panel which is rolled onto the can body flange in the first operation and, in the second operation, the seam is ironed to the required tightness.
It is essential that the final seam is sufficiently tight to ensure compression of lining compound within the seam and consequent hermetic sealing. Other requirements such as sufficient overlap of body and end hooks may also need to be controlled. In manufacturing lines, the repeatability of the production of good seams is clearly also of paramount importance.
In order to ensure that required seam tightness can be both set and maintained so that the seam setting is repeatable over long manufacturing runs, seam adjustment devices are provided.
One known adjuster uses rotation of a worm screw to enable radial movement of a cam follower relative to the seam tool in order to adjust seam tightness. However, as the worm is located at the opposite end of the machine from the seam tool itself, setting and adjusting seam tightness is inconvenient. Furthermore, removal of second operation cam followers is required in order to perform a check on the first operation seam thereby making such inspection a lengthy procedure. Height adjustment of the seam tool is achieved by rotating a threaded seam tool shaft so that the shaft moves vertically. In this adjuster, access is required to both ends of the seaming shank.
This problem of access has been addressed in another adjuster in which a worm thread on the seam tool shaft mates with an adjustment screw for setting seam tightness. Height of the seam tool is varied by a screw adjuster. The screw adjuster has a flange which locates in a groove in the seam tool shaft. Both height and seam tightness adjustment thus act directly on the seam tool shaft. The worm thread on the seam tool shaft for seam tightness setting is therefore oversized so that vertical adjustment is still possible while maintaining mesh with the radial adjustment screw. As a result, some precision in the mechanism is lost and, when unlocking screws to set seam tool height, seam tightness settings may inadvertently be altered.
This invention seeks to overcome the problems of prior art seam adjusters.